WO1985002395A1

WO1985002395A1 - Boria modified alkaline-resistant glass

Info

Publication number: WO1985002395A1
Application number: PCT/US1984/001907
Authority: WO
Inventors: Durai N. Raghavan; Tetsuro Horiuchi; William S. Britt
Original assignee: Atlantic Richfield Company
Priority date: 1983-11-23
Filing date: 1984-11-19
Publication date: 1985-06-06
Also published as: JPS61500491A; EP0162108A1; EP0162108A4

Abstract

Glasses formed from modified naturally occuring zeolites and in particular to fiberizable glasses containing boria. Alkaline-resistant glass fibers are formed from a naturally occuring alkaline earth metal aluminosilicate zeolite material modified by addition of components of alkaline earth metals, boron and aluminium.

Description

BORIA MODIFIED ALKALINE-RESISTANT GLASS

Technical Field The invention herein relates to alkaline- resistant glasses. While it pertains to glass bodies generally, it has particular pertinence to glasses which are fiberizable.

Background Art The natural mineral zeolites are a group of hydrous alkali and/or alkaline earth aluminosilicates which have an open three-dimensional crystalline framework. While a large number of individual mineral zeolites are known and have been described in the literature, eleven (11) minerals make up the major group of mineral zeolites: analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, natrolite, phillipsite and wairakite. The chemical and physical properties of these major mineral zeolites, as well as the properties of many of the minor mineral zeolites, are described extensively in Lefond (ed.), Industrial Minerals and Rocks (4th Ed., 1975), pp. 1235-1274; Breck, Zeolite Molecular Sieves (1974), especially Chapter 3; and Mumpton (ed.), Mineralogy and Geology of Natural Zeolites, Vol. 4 (Mineralogical Society of America: November, 1977). These publications also describe the geologic occurrence of the natural mineral zeolites and some industrial and agricultural uses which have been proposed or in which the natural mineral zeolites are now being used commercially. It is important to note that the natural mineral zeolites are an entirely different class of materials from the "synthetic zeolites" which have been widely described in many recent articles and patents. Because there is no universally recognized system for naming the synthetic zeolites, and because some of the synthetic materials exhibit x-ray diffraction patterns which suggest possible similarities in structure with the natural mineral zeolites, some reports in the literature and patents have described certain synthetic zeolites as "synthetic" versions of the natural mineral zeolites. Thus, for instance, certain synthetic zeolites have been described as "synthetic analcime" or "synthetic mordenite" and so forth. As noted in the aforementioned Breck reference, however, this approach is technically unsound and has merely led to confusion between the two (2) otherwise distinct classes of materials: the natural mineral zeolites and synthetic zeolites. While it has been recognized that there are structural similarities between the two groups, it is clear that the natural mineral zeolites constitute a class of materials significantly separate and distinct in structure and properties from the synthetic zeolites.

Glasses are vitreous materials composed largely of silica. Because silica is a highly refractory material, however, substantial quantities of soda ash, lime or other fluxing materials are added to the silica to permit the glass-forming composition to be melted at reasonable temperatures. Small quantities of other materials, usually elemental materials or oxides, are commonly added to glass melts to provide particular properties such as color or chemical resistance to the finished glass. One experiment has been reported in which a clinoptilolite and glass mixture was fired at 800°C (well below the melting point of either) to produce what was described as a porous low density glass composition; see Mumpton, supra, p. 197, referring to Tamura Japanese published application 74/098,817 (1974).

Alkaline resistance is provided in some glasses by the inclusion of substantial quantities of zirconia and/or titania, such as in AR glasses of Pilkington. Although these materials enhance the alkaline resistance of glass bodies, these are refractory materials which increase the melting point of such glasses. Also, zirσonia and titania tend to add cost to the glass inasmuch as these are much more expensive materials than silica, soda, calcia and the usual components of soda lime silica glasses.

Although calcia tends to lower the melting point of the glass composition, a general admonition exists in the glass technology against using calcium oxide in soda lime silica glasses in quantities greater than about fifteen percent (05%) by veight of the glass body.

Disclosure of the Invention

Objects of the Invention: It is an object of the invention to produce alkaline-resistant glasses from modified, naturally occurring zeolite materials.

Another object of the invention is to modify naturally occurring zeolite materials with readily available boron, aluminum and alkaline earth metal compounds.

A further object of the invention is to form glass bodies from modified naturally occurring zeolites at relatively low temperatures. A still further object of the invention is to form glass compositions having improved properties, in particular, fiberizability and/or alkaline resistance.

Summary of the Invention: The invention herein comprises glass compositions which have good working and forming properties and which have outstanding resistance to alkaline environments. Such glass compositions are characterized by a low boria content, a relatively high calcia content, a relatively low silica content and a moderate alumina content. In one preferred embodiment, these glass compositions are derived from a naturally occurring zeolite to which a boron containing material and at least one alkaline earth metal compound, especially calcium compound or calcium and magnesium compounds, are added to yield a low-silica, high-alkaline earth metal oxide, especially calcia, boria containing glass composition. Alumina or an aluminum compound may be added to the glass-forming materials. Included within the scope of the present invention are glass bodies, particularly fibers, formed from the aforesaid glass composition.

Detailed Description and Best Modes for Carrying Out the Invention

The present invention relates to boria-modified, alkaline-resistant glasses containing relatively high quantities of one or more alkaline earth oxides and particularly to glasses comprising boria, silica, alumina, calcia and combinations of calcia and magnesia. A particularly useful alkaline-resistant glass has the following composition:

Silica - about 30% to about 60% by weight, alumina - about 2% to about 20% by weight, calcia - about 20% to about 60% by weight, magnesia - about 0% to about 30% by weight wherein the calcia plus magnesia content is from about 20% to about 60% by weight, and boria - about 0.1% to about 6% by weight.

In one preferred embodiment, the invention relates to glasses formed from naturally occurring zeolites and especially to glasses wherein such zeolites are present in at least substantial quantities in the glass-forming mixture, often providing the predominance of the glass-formers, in particular, the silica present in such mixtures.

It is significant, as described hereinafter, that such glasses may be easily and inexpensivelly formed by melting a boria-forming material and an alkaline earth metal material, especially a calcium compound, in the form of limestone, for example, or a calcium compound and a magnesium compound, such as found in dolomite, with one or more naturally occurring zeolites. However, glasses of excellent resistance to alkaline attack may be formed by starting with conventional materials such as silica, soda ash, an aluminaforming material, limestone and/or dolomite, and a boria-forming material. Such glasses may be described as low-boria, moderate-alumina, calcium silicate glasses inasmuch as the calcium is generally present in greater quantities than alumina.

The alkaline-resistant glass composition may be readily formed by mixing calcium carbonate with a naturally occurring zeolite material. Many naturally occurring zeolite materials may be formed into glasses under appropriate conditions. Naturally occurring zeolites, as a glass-forming material, have many advantages. Naturally occurring zeolites have already undergone reaction and the various elements are intimately mixed and reacted with one another. Also, the zeolite materials are particularly useful inasmuch as they have a very low sulphur content. In particular, very useful glass bodies may be formed by combining various quanti¬ties of boria and calcia or calcia and magnesia combinations with a zeolite of the following compositional range:

Silica - about 60% to about 85%, alumina - about 6% to about 30%, Fe2θ3 - about 0.1% to about 3%, calcia - about 0% to about 15%, magnesia - about 0% to about 5%, potassia - about 1% to about 2%, soda - about 1% to about 2%, with the percentages expressed being in weight percent.

In particular, it has been found that additions of minor quantities of a boria-forming material and from about 20% to about 60% by weight, and in particular from about 20% to about 50% by weight calcium carbonate mixed with a zeolite of the above-indicated composition results, after melting of the finely ground material, in a glass having good working and forming properties and excellent resistance to an alkaline environment. Furthermore, these glasses advantageously melt at temperatures from about 1250°C to about 1500°C, with selected compositions melting below 1350°C. Also, glasses formed by mixing zeolite and a boria-forming material with similar weight percentages of dolomite; i.e. about 40% to about 80% by weight (based upon weight of zeolite present) of dolomite, result in glasses having comparable properties to those formed by addition of calcium carbonate. Although carbonates are preferred reactants, other salts or compounds of alkaline earth metals, especially calcium and magnesium, could be utilized. In utilizing zeolites with a relatively low alumina content, for example less than about 10% to about 15% by weight of zeolite material, it is preferable to include additional alumina-forming material in the glass-forming mixture to enhance the fiberizability of the resulting glass.

A glass-forming composition may be readily prepared by mixing finely ground boron-containing material and limestone with a finely ground zeolite material, such as the composition identified above. The zeolite material, inasmuch as it is a pre-reacted crystalline material, for example, calcium aluminum silicates, reacts readily and efficiently with the boron-containing material, such as borax, colemanite and the like, and calcium carbonate of the limestone to form a glass composition having a minor boria and relatively high calcia loading. The boron-containing material appears to provide the glass with improved working and forming properties and especially enhances the fiberiz ability of the glass, particularly in conjunction with the presence of a moderate alumina content. The boria-containing glass material, upon cooling, exhibits good physical properties, having strengths and other qualities substantially equivalent to a typical silicate fiber glass and having resistance to alkaline solutions from about ten-fold to about twenty- fold better than a typical soda-lime silicate window glass. Also, the resistance to alkaline materials tends to increase as the calcia content increases from about

20% to about 50% by weight in the glass and then tends to decrease slightly with greater loadings of calcia. Appropriate balancing of addition of a boria-forming material and, preferably, an alumina-forming material and alkaline earth metal components results in formation of a glass having excellent fiberizability without loss of alkaline resistivity.

Besides improving the fiberizability and durability of the glass, glasses containing low boria and moderate to relatively high calcia loadings have other advantages as well. The addition of calcia and/or magnesia, and optionally alumina, tends to even out variances in the zeolite composition. Zeolites are naturally occurring materials and are not homogenous or uniform in their composition.

The zeolites contain relatively substantial quantities of water, that is, hydrated materials. Hydrated crystalline materials generally tend to melt at a lower temperature. Thus, there are further advantages to beginning the glass-forming operation with a prereacted zeolite, rather than initiating it with silica.

The melting temperatures of the boria-modified alumina alkaline earth metal silicate glasses of this invention come within a range, i.e. about 1250°C to about 1500°C, and especially about 1300°C to about 1400°C, which permits the drawing of glass fibers through platinum dies. For example, such glass fibers may be drawn through a platinum or platinum-rhodium die at temperatures of about 1100ºC to about 1350°C. The glass fibers could also be formed by spinning or other techniques. However, formation of continuous strands is best accomplished by drawing through an orifice in a platinum or platinum-rhodium body. A particular advantage of the boria-modified glasses described herein resides in their excellent working and fiber-forming properties, their resistance to crystallization and uniform viscosity across a broad temperature range at fiber-forming temperatures.

Fibers of the glass compositions of this invention are particularly useful inasmuch as they may be used to strengthen bodies which are highly alkaline in nature, for example, cement and plaster. Such fibers may also be used to strengthen organic matrices of various types. Reinforcement of cement with such fibers, however, provides a particularly advantageous use inasmuch as asbestos has been frequently used heretofore for that purpose. Because of various health and/or environmental concerns, the use of asbestos is being discontinued. Continuous strands or mats of glass fibers having the glass compositions described herein effectively reinforce concrete bodies.

EXAMPLE I

Glass-forming materials were finely comminuted, admixed with particulate additives as identified in the following tables (expressed in percent by weight) and melted to form glass bodies and fibers. The melting was conducted batch-wise in small crucibles at temperatures of about 1250°C to about 1500°C depending upon batch composition and quantity of additives.

The glasses set forth in Table I were prepared from silica, alumina, calcium carbonate, boria and magnesium carbonate. A zeolite material was not present in the batch. These glasses were prepared from traditional glass-forming materials in order to examine the fiber-forming, alkaline resistance and other properties of the resulting glasses.

Glass Ic exhibited very good properties. Its melting point was reasonably low while its alkaline resistance was very good. Fibers were formed without difficulty.

Glasses IIa and lIb exhibited excellent alkaline resistance; however, fiberizability and working range were not within preferred parameters. Glass lIc exhibited an improved working range over Glasses Ila and lIb, although the alkaline resistance was lower.

Glasses IlIa through IIIe exhibited excellent alkaline resistance and metling temperatures. GlassesIIId and IIIe exhibited excellent fiberizability and working temperature range although their alkaline resistance was slightly less than Glasses IlIa through

IIIc.

Glass fibers formed from glasses Illb, IIIc and IIId are excellent reinforcement materials for concrete. Fiber loadings in cement and concrete of from about 1% to about 10% by weight, and in particular around 5% by weight, enhance the strength of the concrete without significant degradation of the fiber.

The glasses identified in Table II and III throughout the present Example were prepared from a zeolite having the following composition:

SiO₂ 82.8 percent by weight

AI₂O₃ 8.4 percent by weight Fe₂O₃ 0.3 percent by weight

CaO 0.9 percent by weight MgO 0.6 percent by weight

K₂O 2.9 percent by weight

Na₂O 4.1 percent by weight

Minor variations in the composition may occur from batch to batch of the zeolite. Very minor quantities of other elements, for example boron, manganese, zirconium, titanium, vanadium, antimony, barium, in combined form, may be present in such a naturally occurring zeolite. The quantities of such materials generally are individually below about 0.1% by weight and are usually less than 0.01% by weight and frequently present in amounts less than 0.005% by weight. Various other materials, especially those having metallic elements, may be found in trace amounts in the zeolite material. The glass fibers of the above example were continuously drawn through a platinum bushing at bushing temperatures of about 1200°C from molten glasses formed from calcium-carbonate-modified naturally occurring zeolites wherein the modifications included various additions of an aluminum component, a boron component, an alkaline earth metal component and, optionally, a zirconium component.

It is significant that the above-identified glass compositions are fiber-forming and have excellent mechanical properties, such as tensile strength, comparable to commercial glass fibers while possessing outstanding alkaline resistance. These modified zeolite glasses are relatively low in iron content and possess an unobjectionable light green color.

In forming the alkaline-resistant boria-containing glasses of this invention, it is preferred, if starting with a zeolite material, to have such zeolite material present at least about 35% by weight of the glass batch mixture. If the zeolite provides substantially all the silica component for the resulting glass, then quantities of 40% to 50% by weight or more of the zeolite may be utilized in the glass batch mixture.

The glass batch mixture contains a significant quantity of a boria-forming ingredient, such as borax, colemanite, sassolite, ulexite and the like. Various naturally occurring borosilicate materials or borosilicate or boroaluminosilicate glass cullet, of course, may be utilized to provide the boron component in the glass batch. The boron-containing component is usually present in the glass batch in quantities of up to about 6% by weight and is typically present in sufficient quantities to provide a boria content in the resultant glass of from about 0.1% to about 6% by weight and preferably from about 1% to about 5% by weight and especially preferred from about 1% to about 4% by weight. Although the instant invention relates particularly to the preparation of alkaline resistant fiber glasses from glass batches containing substantial quantities of a zeolite material and especially to a mixture of a zeolite material and additional aluminum and alkaline earth metal components to which a boron component is additionally included, certain unique glass compositions disclosed herein may be formulated from glass batches containing no zeolite. Such glass compositions have unique properties, including fiberizability and alkaline resistance. One such glass composition is as follows, expressed to the least significant number as percent by weight.

SiO₂ 45-55 AI₂O₃ 12-20

Fe₂O₃+FeO <1. 0

CaO 20-35

MgO 0-10

K₂O 0-5 Na₂O 0-5

B₂O₃ 0.1-6 wherein CaO + MgO is 20-40.

A preferred composition is as follows, expressed to the least significant number as percent by weight:

SiO₂ 46-54

AI₂O₃ 12-16

Fe₂O₃+FeO <1.0

CaO 22-35 MgO 0-4

K₂O 0-4

Na₂O 0-4

B₂O₃ 1-4 wherein CaO + MgO is 22-35. One particularly preferred composition contains about 26-30% by weight calcia wherein CaO + MgO is about 26-34% by weight. An especially useful composition has the following oxide content, expressed to the least significant number as percent by weight:

SiO₂ 45-49 AI₂O₃ 12-16

Fe₂O₃+FeO <1.0

CaO 25-30

MgO 0-3

K₂O 0-3 Na₂O 0-3

B₂O₃ 1-4 wherein CaO + MgO is 25-33.

Although excellent fiberizability is a characteristic of all of the glasses set forth in the immediately preceding compositions, the alkaline- resistance of such glasses varies with the quantity of boria present. Generally, glasses having less boria have better alkaline resistance. Thus, in glasses having a lower calcia content, the boria content should be low in order to maintain excellent alkaline resistance. While glasses containing about 30% by weight calcia can have up to about 6% by weight boria, glasses containing about 22% by weight calcia should contain less than about 2% by weight boria to exhibit good alkaline resistance. (Good alkaline resistance, for the purposes of this invention, is a loss of less than about 3.3% by weight of a glass sample in 5% NaOH at 90°C for 72 hours.)

In the above recited compositions, minor quantities of zirσonia and titania , for example up to about 2% by weight, may be present. The above stated compositions may be formed, of course, from modified zeolites without loss of any outstanding properties. Industrial Applicability The outstanding tolerance to alkaline environments render these glasses, especially in fiber or flake form, as excellent reinforcement materials for concrete, piaster: and other inorganic matrices of an alkaline nature. This is especially significant inasmuch as asbestos, which has been a standard extender as reinforcement material in cement and concrete bodies, is considered undesirable because of the health hazard it may present.

Glass fibers formed from glasses of this invention have particular utility as a reinforcement material for cementatious bodies, e.g. cement and concrete. Cementatious bodies exhibit enhanced strength when such bodies are reinforced with a minor amount of glass fiber, preferably from about 1% to about 10% by weight, and more preferably about 1.5% to about 7.5% by weight glass fibers of the type described herein. The fibers are included in cementatious bodies in sufficient amount to enhance the strength of such bodies.

The glasses of this invention have excellent resistance to moisture degradation and do not degrade or deteriorate during normal or extended storage periods.

The low sulfate content of naturally occurring zeolites is important in their utilization as ingredients in glass-forming processes. Sulfates tend to degrade during glass melting conditions, yielding sulfur dioxide and other objectionable sulfur compounds. Environmental concerns militate against use in glass-making processes of any raw material containing sulfates, sulfites and other sulfur compounds.

Although the instant invention has been described as boria-containing glasses having relatively high loadings of calcia, it is to be recognized that at least minor substitutions of other alkaline earth metal oxides in lieu of calcia may be made. For example, magnesium compounds, particularly magnesium carbonate may be substituted for at least some of the calcium carbonate in preparing a batch tor melting into an alkaline- resistant glass. Similarly, barium and strontium compounds may be substituted as well as beryllium compounds, many of which are naturally occurring materials found in the same geographic regions as zeolites. The oxides of alkaline earth metal elements are not considered glass formers, which is a terra applied to elements having a valence greater than three, e.g. silicon, boron, andphosphorous, which may form three-dimensional networks with their oxides, namely, silica, boric oxide, and various oxides of phosphorous. Alkaline earth metal elements, being divalent, are more tightly bound in a glass than are alkali metal elements.

Sources of alkaline earth metals to form oxides in the glasses of this invention are as follows: Alkaline Earth Metal Compound Source

Calcium Carbonate Limestone

Marble Chalk

Magnesium Carbonate Dolomite Magnesium Silicate Serpentine

Barium Carbonate Wetherite

Strontium Carbonate Strontianite

Beryllium Aluminum Silicate Beryl

Sources of calcium and magnesium carbonates are generally more plentiful and cheaper than sources of barium, strontium or beryllium compounds. Also, beryllium metal is considered toxic, although beryllium oxides bound within a glass body are not hazardous. Aluminum may be included in the glass batch as alumina, aluminosilicates, e.g. from aluminosilicate glass cullet or as naturally occurring materials such as various clays includ kaolin, montmorillonite and the like.

Zirconia ma optionally, be present in the fiber glass composit; of this invention. Minor quantities of zirconi may occur in some compositions trom melting the glass batch mixture in zirconia-containing crucibles. Also, a zirconium-containing component may be added in the form ot zircon, various zirconium silicates and as zirconia-containing cullet.

It is noteworthy that the boron-modified, zeolite-derived glasses of this invention have good working properties and strength in addition to outstanding alkaline resistance. These glasses may be used in any form, e.g. containers, sheets, fibers and the like, and especially for any use in which transparency or colorlessness are not required. The glasses may be used as flakes, bubbles Cmicrospheres), fibers and the like to reinforce organic or inorganic matrices, especially cement, plaster and the like. The characteristics of the glasses of this invention are particularly adapted to the formation of alkaline resistant fibers.

Claims

1. A glass-forming mixture comprising a substantial quantity of naturally occurring pre-reacted zeolite material and a minor quantity of a boron compound capable of forming boria under glass-forming conditions.

2. An alkaline-resistant glass composition comprising about 30-60% by weight silica, about 2-20% by weight alumina, about 20-60% by weight calcia, about 0-30% by weight magnesia, and about 0.1-6% by weight boria, wherein the calcia plus magnesia content is about 20-60% by weight.

3. A method of forming a glass having the composition set forth in Claim 2 comprising melting a naturally occurring zeolite material, an aluminum component, an alkaline earth metal component and a boron component.

4. The mixture of Claim 1 wherein the pre-reacted zeolite contains substantial quantities of silicon, aluminum and calcium components capable of forming silica, alumina and calcia under glass-forming conditions.

5. The mixture of Claim 1 wherein said zeolite provides a substantial portion of the siliceous material in the mixture.

6. The mixture of Claim 1 wherein the zeolite is present as at least about 35% by weight of said mixture.

7. The mixture of Claim 1 wherein a boron-containing component capable of forming boria under glass-forming conditions is present in the mixture in quantities up to about 10% by weight of the mixture.

8. The mixture of Claim 1 wherein significant quantities of aluminum and calcium components capable of forming alumina and calcia under glass-forming conditions are added to the mixture.

9. The glass composition of Claim 2 wherein the composition comprises:

SiO₂ - about 45% to about 55% by weight;

AI₂O₃ - about 12% to about 20% by weight;

FeO+Fe₂O₃ - less than about 1.0% by weight;

CaO - about 20% to about 35% by weight; MgO - about 0% to about 10% by weight;

K₂O - about 0% to about 5% by weight;

Na₂O - about 0% to about 5% by weight;

B₂O₃ - about 0.1% to about 6% by weight; wherein CaO + MgO is about 20% to about 40% by weight.

10. The glass composition of Claim 9 wherein the composition comprises: SiO₂ - about 46% to about 54% by weight; AI₂O₃ - about 12% to about 16% by weight; FeO+Fe₂O₃ - less than about 1.0% by weight; CaO - about 22% to about 35% by weight; MgO - about 0% to about 4% by weight; K₂O - about 0% to about 4% by weight; Na₂O - about 0% to about 4% by weight; B₂O₃ - about 1% to about 4% by weight; wherein CaO + MgO is about 22% to about 35% by weight.

11. The glass composition of Claim 2 wherein the composition consists essentially of: SiO₂ - about 45% to about 49% by weight; AI₂O₃ - about 12% to about 16% by weight; FeO+Fe₂O₃ - less than about 1.0% by weight; CaO - about 25% to about 30% by weight; MgO - about 0% to about 3% by weight; K₂O - about 0% to about 3% by weight; Na₂O - about 0% to about 3% by weight; B₂O₃ - about 1% to about 4% by weight; wherein CaO + MgO is about 25% to about 33% by .weight.

12. The method of Claim 3 wherein said melting is conducted at a temperature of about 1250°C to about 1500°C.

13. The method of Claim 3 wherein glass fibers are formed from the molten glass by drawing same through a platinum or platinum-rhodium die at a temperature of about 1100°C to about 1350ºC.

14. The method of Claim 3 wherein the naturally occurring pre-reacted zeolite is present in the mixture as at least about 35% by weight of said mixture.

15. The method Claim 3 wherein the boron component is selected from the class consisting of borax, colemanite, sassolite and ulexite.

16. A cementatious body containing a minor amount of glass fibers of the composition of Claim 1.

17. The body of Claim 16 wherein said fiber is present from about 1% to about 10% by weight of said body.

18. The body of Claim 16 wherein said glass fiber is present from about 1.5% to about 7.5% by weight of said body.

19. A cementatious body containing a minor amount of glass fibers of the composition of Claim 2.

20. The body of Claim 19 wherein said fiber is present from about 1% to about 10% by weight of said body.

21. The body of Claim 19 wherein said fiber is present from about 1. 5% to about 7. 5% by weight of sa id body.

22. A cementatious body containing from about1% to about 10% by weight of said body of glass fibers of the composition of Claim 9.